This is a bit of a continuation from my last thread (
http://www.c3vr.com/vrforums/master-cylinder-question_message421197.html ) but this question is more specific to brake bleeding so I started a new thread. Anyway, I can't seem to get the fronts bled properly - they just spit a little fluid, no solid flow at all, no matter how many times I do the pump and bleed. (I asked my wife to do some pedal pushing tonight) I've also supplied the bleeder with a generous vacuum source and same thing - it will pull some fluid through but not much. It almost seems like there is a blockage somewhere. Could this have anything to do with the proportioning valve? I didn't touch it, but did disconnect, remove, and re-install the line that goes from the valve to the right front wheel.

Other stuff I've done:

New (reman) master cyl (could that be the problem? I did bench bleed)

Rebuilt front calipers with new seals

New rubber lines in front

Stuff I have not done:

All original steel lines, all in good shape (at least outside)

Did not touch back calipers. Pads are good and no signs of leakage

Backs seem to bleed out fine (inboard and outboard) - nice solid flow when bleeder is opened. But pedal is still soft and goes all the way to the floor.

Sometimes the threads around the bleeders will allow air back into the system. I had to put some thread sealer on mine and the bubbles stopped - solid stream of fluid. Also make sure not to open them too far. 1/4 turn should do it.

If that's not it and they are new calipers, you have to have something going on further up the line Dave.

I'd be leanin towards the proportioning valve, too. It's possible that it has flopped. SOMETIMES, you can pop the brake pedal HARD, and get the valve centered again.Does your red brake light in the dash work, and if it does, is it staying ON?

Thanks, guys. I'll focus my attention on the pro valve next. Any suggested vendors for a replacement? I've even had a hard time finding one on some of the online catalogs - I guess some call it a "distribution block" others "proportioning valve" and still others "proportion valve". Would love to know where others have purchased theirs.

Joel, the brake light works as it should - comes on when the e-brake is pulled up, but is off otherwise. I just went out and hit the pedal hard a few times, but no change. Any thoughts? Should I still be looking at the pro valve?

daveo76 said: Thanks, guys. I'll focus my attention on the pro valve next. Any suggested vendors for a replacement? I've even had a hard time finding one on some of the online catalogs - I guess some call it a "distribution block" others "proportioning valve" and still others "proportion valve". Would love to know where others have purchased theirs.

Joel, the brake light works as it should - comes on when the e-brake is pulled up, but is off otherwise. I just went out and hit the pedal hard a few times, but no change. Any thoughts? Should I still be looking at the pro valve?

Dave, I just got done bleeding my brake and my blood.......actually my sweat. I would rather pull the engine/transmission and body than do the brakes again. I did them myself.....tough to do. I had previuosly bench bled my new master cylinder in the vise. I have completely new stainless steel brake lines and new brass diverting blocks. Also all new stainless steel flex hoses. I had flow to the front brakes. There are actually two bleeders on all 4 calipers. The rear brakes I couldn't get any flow. I even opened the connection off of the proportioning valve. I then connected up a pressure power bleeder to the MC. I pumped up the pressure to 15 psig. I left the bleeders completely out of the rear calipers. I finially got flow to the rear by pumping the pedal. I'm using dot 5 silicone fluid (purple). I put the Russell check valve bleeders back in and opened individually each one less than a quarter turn. I pumped slowly in on the brake petal and held it down for at least 10 seconds. I did this for all 4 bleeders in the rear about twelve time apiece. I then went back to the fronts and repeated the same procedure. I almost filled a Mason jar with the purged brake fluid. When I came into the house my wife had to dry off my sweat when she saw me (she's a keeper). Well anyhow that's about the worst job of my project so far. I sure hope everything works out for you. Oh and by the way the pedal is as hard as a rock

Well, you're definitely a step or two ahead of me! Glad you've got a hard pedal now after all that effort. Hopefully I'll be there soon, but I took a step backward tonight. Removed the M/C and the proportioning valve. I'm going to re-bench-bleed my M/C and also make sure the lines and calipers are full of fluid before I go on.

Thanks for the input on the proportioning valve, guys. I know this may be bucking conventional wisdom, but can those puppies be re-conditioned? They're expensive prolly because they're basically a hunk of solid brass. The only somewhat complicated part is the little piston that moves back and forth and mine seems to move freely (prolly 1/4" or 3/8" travel?). I was going to replace the two o-rings I found and I tested the switch part - continuity in the pressed condition and no continuity un-pressed. I'll also blow out the passages with air. Anything else that can go wrong? I'll replace it if needed, but would hate to put a new one for no reason.

Thanks for the input on the proportioning valve, guys. I know this may be bucking conventional wisdom, but can those puppies be re-conditioned? They're expensive prolly because they're basically a hunk of solid brass. The only somewhat complicated part is the little piston that moves back and forth and mine seems to move freely (prolly 1/4" or 3/8" travel?). I was going to replace the two o-rings I found and I tested the switch part - continuity in the pressed condition and no continuity un-pressed. I'll also blow out the passages with air. Anything else that can go wrong? I'll replace it if needed, but would hate to put a new one for no reason.

Dave be very careful on the material of the O rings. Just make sure it's compatable with American brake fluid. Years ago I had an MG and used American brake fluid. The British used natural rubber in the MC, which turn into gum. Not long after the fluid addition.............I was without brakes. It takes a lot of white knuckle driving to make it home with no brakes. I then rebuilt my MC. It's not very hard to do. The only special tool needed is a hone to reface the cylinder. Buna N does work with Dot 4 fluid. Just make sure they are not real rubber, and also make sure to use the proper ID OD and thickness of the rings

Don't know if this could be your problem or not but I replaced my leaking master cylinder with a rebuilt O'reilly's a couple of weeks ago. Could never get a firm pedal after bleeding 3 times. It would almost go to the floor, sorta like stepping on a ripe plum (courtesy of C W McCall. lol). Drove the vette over to close to Dallas for a bunch of major work. Almost there, traffic stopped due to an accident. I hit my brakes...and guess what! NOTHING..TO THE FlOOR! Luckily there was a median strip between the concrete wall an the two lanes of stopped traffic in front of me. Long story short... the master cylinder was CRAP! Might want to consider that as possibly your problem

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I know the voices aren't real, but they have some pretty cool ideas...

Another wild idear I have on it....take the bleeders out of the front calipers completely, and see if the holes for the fluid where the bleeders thread in are stopped up. I have definitely seen this in calipers, both rebuilt, and old ones on the car. Crud builds up there over time, and sometimes, it just won't allow fluid to pass thru the bleeders. I'm not talking about the bleeders themselves, but the holes in the calipers. But...I have also seen bleeders that were crudded up enough to not allow flow.Just because the calipers are rebuilt doesn't mean they were cleaned really well before.It's worth a look-see, anyway.

It's interesting to see the research tangents I get to go on for this car. Tonight I got to research o-ring material types that are compatible with DOT 4 brake fluid, thanks to Corvette440! I came up with a little bit different info, though: most sources said to stay away from Buna N (also known as nitrile) and use something like EPDM, which I have no clue where I'd get a "variety pack of" those. I'm using Valvoline synthetic DOT 3&4 and interestingly, they say that fluid is actually compatible with natural rubber! (http://www.valvoline.com/pdf/valvoline_brake_fluid.pdf) I think most of the o-rings you get at the parts store or hardware store, though, are just regular old nitrile. The existing o-rings look like they're still OK so if I can't find any EPDM I may just put it back together with the originals (after I blow out the passages)

Joel, caliper bleeder holes look OK. Tonight I flushed through the pipe that goes from the valve to the right front and then separately flushed through that caliper. I think I'm OK there, but I ain't ruling anything out yet. Same goes for the M/C. Since I have it off I may just go take it back and try a different one. A coworker swears that is my problem - he said he had a similar problem with a new M/C and swapped it out and problem solved. Wasn't a Corvette, though, or even a GM. Thanks for the suggestions guys and I'll keep y'all in the loop.

The ethylene content is around 45% to 75%. The higher the ethylene content the higher the loading possibilities of the polymer, better mixing and extrusion. Peroxide curing these polymers give a higher crosslink density compared with their amorphous counterpart. The amorphous polymer are also excellent in processing. This is very much influenced by their molecular structure. The dienes, typically comprising from 2.5% up to 12% by weight of the composition, serve as crosslinks when curing with sulphur and resin, with peroxide cures the diene (or third monomer) functions as a coagent, which provide resistance to unwanted tackiness, creep or flow during end use.

The main properties of EPDM are its outstanding heat, ozone and weather resistance. The resistance to polar substances and steam are also good. It has excellen

Typical properties of EPDM vulcanizates are given below. EPDM can be compounded to meet specific properties to a limit depending first on the EPDM polymers available, then the processing and curing method(s) employed. EPDMs are available in a range of molecular weights (indicated in terms of Mooney viscosity ML(1+4) at 125 °C), varying levels of ethylene, third monomer and oil content.

it has electrical insulating properties.

Typical properties of EPDM vulcanizates are given below. EPDM can be compounded to meet specific properties to a limit depending first on the EPDM polymers available, then the processing and curing method(s) employed. EPDMs are available in a range of molecular weights (indicated in terms of Mooney viscosity ML(1+4) at 125 °C), varying levels of ethylene, third monomer and oil content.( This was copied from wikipedia)

I was also wondering if Vitron (green) O rings would work. Vitron is sold at auto parts stores. They have variety packs. These O rings are used for Aircondioning seals that use sythetic oil (POE) for R134A. I purchased a packet at Advance

Yep, I ran across some of those green ones in a variety pack yesterday at a parts store. They were listed as HNBR, which I think is also used for A/C with R134a. (HNBR is a "hydrogenated" version of NBR or Buna-N). But I think Viton ones are also green or have a green stripe and can be used for A/C. BUT, it seems like NEITHER is appropriate for glycol based (DOT 3&4) brake fluids. (I included a link I found to a comprehensive guide to rubber types below) I think I need EPDM, but I'm pretty sure I'd have to order them online somewhere. BUT, I decided to just put the valve back together with the original o-rings since they were in pretty good shape.

So I put the valve back together (cleaned with canned air) and re-installed it and tomorrow I'm going to try to take the M/C back. Hopefully I can get everything back together, re-bleed and come up with a firm pedal. Wish me luck!

Yep, I ran across some of those green ones in a variety pack yesterday at a parts store. They were listed as HNBR, which I think is also used for A/C with R134a. (HNBR is a "hydrogenated" version of NBR or Buna-N). But I think Viton ones are also green or have a green stripe and can be used for A/C. BUT, it seems like NEITHER is appropriate for glycol based (DOT 3&4) brake fluids. (I included a link I found to a comprehensive guide to rubber types below) I think I need EPDM, but I'm pretty sure I'd have to order them online somewhere. BUT, I decided to just put the valve back together with the original o-rings since they were in pretty good shape.

So I put the valve back together (cleaned with canned air) and re-installed it and tomorrow I'm going to try to take the M/C back. Hopefully I can get everything back together, re-bleed and come up with a firm pedal. Wish me luck!

Fingers and toes crossed for you Dave. If it don't work go for the pressurized MC setup..........I think that's plan C.

Thanks, Larry. The digit crossing didn't work out for me - still have a soft pedal. BUT, I think I'm making headway. I found a serious problem on the fronts: I did not install the hoses with the copper washer at the caliper. With my vacuum pump I think air was being sucked in through that interface. There is still another problem, though. I'm pretty sure my prop valve is off-center again. When I was working on them earlier today I did the rears first. I actually had some pedal after I was done with those. But then I moved on to the front and with the lack of pressure in that circuit I think the valve got off center. I can tell by the fact that I have a full M/C, lid is loose, and no fluid is even dripping out of the disconnected hard line where it would attach to the front left hose. So anyway, tomorrow I will buy some copper washers, put everything back together and try again! I'm hoping I can get the valve re-centered by opening the back bleeders and slowly pushing the pedal. We'll see. Still realize that guy might need to be replaced.

Not installing the hoses with the copper washers is embarrassing. I should have caught that. But I'm also a bit annoyed at Zip - those should be included when you buy new hoses. Not blaming them, my mistake, but how much could it cost to include two washers with a set of front hoses? I think I'm done with those guys for awhile - I had a customer service issue with them a few months ago and it was never really resolved. They gave me a tech guy's contact info, but I must have left two or three messages for the dude and he never even tried to return my call.

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